Buckling Behavior and Design Optimization of Stiffened-Aluminum Cylindrical Shells under External Pressure

Ring stiffeners are preferably used to enhance thin-walled cylindrical shell buckling resistance while subjected to external lateral pressure. A comprehensive finite element (FE) numerical study investigated the influence of geometric and stiffener properties on the critical buckling pressure for aluminum-made ring-stiffened cylindrical shells under uniform external pressure. For validation purposes, 10 ring-stiffened cylindrical specimens were modeled using an ANSYS workbench 2022 whose stiffener dimensions varied so that all specimens' overall weight remained constant. FE linear buckling results were substantiated by the experimental work and the theoretical formulas in the literature. Imperfection sensitivity analysis proves that the stiffened cylindrical specimens under external pressure are less sensitive to imperfection. An optimization study was conducted to achieve the optimal stiffener dimensions by considering 182 specimens such that the overall cylindrical weight remained the same for all specimens. It reveals that linear buckling pressure improves by considering optimum stiffener dimensions. A further parametric study was conducted by considering 350 sample specimens with different radius-to-thickness (R/t) ratios, stiffener's area/tank radius, l/R, and shell thicknesses. A parametric study reveals that the stiffened cylindrical shells with a lower R/t ratio give higher buckling strength; however, linear buckling strength significantly decreases as the R/t ratio increases. Moreover, the linear buckling strength can be gained by increasing the stiffener area and by increasing the shell thickness, with a more pronounced effect observed in tubular specimens. The shell thickness, R/t ratio, and relative stiffener area are the most critical parameters affecting the buckling strength. The specimens with middle-range stiffeners give higher buckling strength, indicating that the optimum choice of ring stiffeners should be considered in the stiffened cylindrical shell structures to obtain higher buckling strength.